cooling problem on my 96' 240sx.... help!!!

[johndavid400]

OK, so I have been noticing a slight leak from my car in the garage over the last week. It is just about a tablespoon or two of coolant that leaks out after each night. Today, the 'check engine' light came on, and then it started heating up (the temp. gauge went almost to the red). So I check the coolant level and it is about 2" from the top, but completely covering the radiator fins inside the radiator, so I head over to get the code checked at autozone and it says "check coolant level". Now while I was driving through town, it would start to heat up, but as soon as I hit the interstate and began going 60-70mph, the temp gauge went way down to the normal operating range.

I was thinking that the problem has to do with one of two things. Either the water pump or the thermostat (since when I briefly looked, I saw no cracked or leaking hoses... and it hasn't been below 40 degrees this month). I thought it might be the water pump or maybe just the gasket on the water pump. Since when I start pushing higher RPM's, it starts pumping the coolant and the temp goes down. I do not have the time right now to go outside and get under the car to check everything (I am 1.5 hrs away from my house, visiting a friend and have no jack or tools with me), but does this sound like a probable cause, given the symptoms? When I get home Sunday, I am going to do a full inspection and replace whatever is necessary, so what do you guys think it might be?

Also, Is the water pump on this car driven by the timing chain or the fan belt pulleys? On some of my other cars, it was on the timing belt, but my Chilton manual says that it is on the fan belt pulleys on the Altima but it didn't say for the 240sx (I know they are the same engine, so I'm guessing that is the same also).

Any help is GREATLY appreciated! thanks in advance

[navysnail]

the cooling system uses pressure to increase the boiling point of the coolant. if there is air in it, it may not be able to properly atain or maintain that pressure required for proper opperation. the 240's water pump is indeed run by the fan belt on the engine. i would advise you to make sure the system is bled (there is a screw on the intake manifold that you remove while you fill it, dont overtighten it though, the manifold is aluminum.)on your way home, you can top it off, but the engine must be cool before you can open the cap, otherwise you will be seriously injured.

finaly, take a good look at all your hoses and connections, as well as the radiator to find out where it is leaking from,

[johndavid400]

see, thats the thing, if it were just a leaky hose, it would still be cooling fine in traffic since there is plenty of coolant in the radiator....... but it isn't cooling fine in traffic, it only starts cooling down after I start running at 3k rpm. I don't see how any air could have gotten in the system, since it has been fine for over a year and I have never even checked the coolant until today (after I noticed the problem). So that is why I think it might be the water pump.... but I am not positive. Does it still sound like a broken hose or something similar? I don't think that it is, but I have no idea....

[navysnail]

well, coolant has to get from the engine block to the radiator, and so that can cause a problem if it is low, and if there is low coolant, air has to have taken its place at the top of the system. fill it all the way up and try to drive back if you have to, but if it is a hose, you wont need any tools to fix it short of a screw driver or possibly a 10mm wrench

[johndavid400]

yah, I didn't think about that...... I guess it could have gotten some air in it that way. But if it is the bottom hose, won't I have to drain all the coolant out before replacing the hose and refilling it? If so, what steps do I take to bleed the air out once I finish replacing the hose?